With each successive semiconductor technology generation, wafer diameters tend to increase and transistor sizes decrease, resulting in the need for an ever higher degree of accuracy and repeatability in wafer processing. Semiconductor substrate materials, such as silicon wafers, are processed by techniques which include the use of vacuum chambers. These techniques include non plasma applications such as electron beam evaporation, as well as plasma applications, such as sputter deposition, plasma-enhanced chemical vapor deposition (PECVD), resist strip, and plasma etch.
Success metrics for a plasma processing system include throughput and substrate temperature stability. Substrate temperature affects critical dimensions of devices fabricated on a substrate and thus must not significantly drift when stable substrate temperature is required, e.g. within a step in a processing recipe. On the other hand, optimum substrate temperature can be significantly different for different process steps within a process recipe. The rate of change in substrate temperature directly impacts the throughput. Therefore, a capability of quickly changing substrate temperature between process steps while maintaining stable substrate temperature within a process step is desirable. Electrically-based heating approaches are complicated by the need for compatibility with radio frequency energy used in a plasma processing system, requiring custom filtering to protect power and control systems for electrical heaters. Design and implementation challenges also exist regarding power connections. In addition, challenges involving heater layout to optimize thermal uniformity can be significant.